A major cause of chronic, and often disabling, back pain is disruption or degeneration of an intervertebral disc. The spine is comprised of bony vertebrae separated by intervertebral discs. Each intervertebral disc connects adjacent vertebrae and forms a form of joint that allows movement of the vertebral column. An intervertebral disc is generally divided into two regions: the nucleus pulposus and the annulus fibrosus. The nucleus pulposus is a gelatinous-like tissue that lies at the center of the disc and provides a cushion between adjacent vertebrae. The annulus is made up of collagen fibers that form concentric lamellae that surround and contain the nucleus pulposus.
There are many causes of disruption and degeneration of intervertebral discs, which can be broadly categorized as mechanical, genetic and biochemical. Mechanical damage includes herniation in which a portion of the nucleus pulposus projects through a fissure or tear in the annulus fibrosus. Genetic and biochemical causes usually result from changes in the biochemical processes of a disc. Such changes can be attributed to genetic disorders or environmental influences. Degenerative disc condition is commonly caused by a change in the biochemical process of an intervertebral disc. Such degeneration is a progressive process that usually begins with a decrease in the ability of the nucleus pulposus to absorb water. With a loss of water content, the nucleus becomes dehydrated, resulting in a decrease of internal disc hydraulic pressure, and ultimately to a loss of disc height. This loss of disc height can cause the annulus to buckle, eventually resulting in annular fissures and ruptures. Herniation occurs when a rupture leads to protrusion of the nucleus pulposus through the annulus.
Furthermore, disc height plays an important role in the functionality of the intervertebral disc and spinal column, and changes in disc height can have both local and wider effects. On the local (or cellular) level, decreased disc height may result in increased pressure in the nucleus pulposus, which can lead to a decrease in normal cell operation and an increase in cell death and disintegration. In addition, increases in intra-discal pressure may create an unfavorable environment for fluid transfer into the disc, which can cause a further decrease in disc height.
Decreased disc height also results in significant changes in the larger mechanical stability of the spine. With decreasing height of the disc, the facet joints bear increasing loads and may undergo hypertrophy and degeneration. Decreased stiffness of the spinal column and increased range of motion resulting from loss of disc height can lead to further instability of the spine, as well as back pain.
Several disc defects may be treated by implantation of a prosthetic into the nuclear space of the intervertebral disc. Some procedures that may include insertion of a prosthetic into the disc are spinal fusion and disc repair and replacement. Prior to implantation of most prostheses, a discectomy is often performed to prepare the nuclear space for implantation of the prosthetic and, when spinal fusion is desired, to facilitate bony fusion between the vertebral bodies. Some implantation procedures may require a total discectomy in which the majority (and usually all) of the volume of the nucleus pulposus is removed. Others may require a partial discectomy in which only a portion of the nucleus pulposus is removed.
Traditionally, when a fusion is the desired treatment option, there are several approaches to access the disc space and position an implant to regain the proper disc height. For a typical posterior surgical approach, an incision is made through the back of a patient and access to the disc space is achieved. Manual instruments are used and inserted through the access to the intervertebral disc requiring treatment. The curettes and rongeurs are used to cut, tear, and remove nucleus pulposus tissue one piece at a time, and the rasps are utilized to roughen or scrape the endplates of adjacent vertebrae. Other options have been disclosed previously to provide a more accurate and minimally invasive disectomy such as disclosure “Disc preparation tools and methods using the same” U.S. application Ser. No. 62/021,960, filed Jul. 8, 2014.
Once the disc has been removed, the implantation of the intervertebral implant device can be achieved. Such devices and methods have also been previously disclosed in application “Device for treating the Spine” U.S. application Ser. No. 12/035,298, filed Feb. 21, 2008, and more particularly, in application “Spinal fusion implants and devices and methods for deploying such implants” U.S. application Ser. No. 13/803,322, filed Mar. 14, 2013 and incorporated by reference herein.
A further component needed in the fusion process to create bony fusion between the two vertebral bodies and that is bone graft material or bone filler material (both of which are generally referred to herein as graft material). Such material will favor the creation of a bony bridge that spans across the implant and connects the inferior (lower) cartilaginous endplate of the superior (upper) vertebral body to the superior (upper) cartilaginous endplate of the inferior (lower) vertebral body.
Traditionally, the graft material (bone graft material and/or bone filler material) is positioned into the implant, such as a cage, prior to insertion into the disc space and due to this process cannot be fully optimized for best endplate to endplate contact.
In addition, previous graft delivery systems are back-loading, such that the graft material must be advanced a great distance through the barrel before it is extruded into the delivery site. More work (force applied over a greater distance) is therefore required to achieve this successfully, and often the nature of the graft material may cause significant binding when pushed over longer distances, rendering the device unusuable.
Minimally invasive spinal surgery requires that all surgical tools be as small as possible to minimize tissue trauma and exposure to the surgical site. Tools to deliver bone graft that have a delivery diameter of 10 mm or less are highly susceptible to requiring large forces to deliver the bone graft material or, in the worst case, may seize entirely because of the high resistance developed when pushing materials of large, irregular grain size like autograft bone graft material. This susceptibility to seizing is aggravated by the length over which the graft must be delivered down the tool, which is typically 6 or more inches if the material is loaded at the most proximal tube position and pushed all the way to the delivery site.
Typical bone graft tools incorporate a proximal funnel, a long tube length, and a manual tamp that requires the user to tap to deliver the graft to the site. Large bone chips loaded into the tube chamber can contribute significantly to delivery resistance. To overcome the resistance, the outer diameter of the delivery tube is often quite large (>10 mm). Further, the loading of these long-bored funnels must be done at the surgical site, lest the material fall out at an undesirable location. Thus, this requires the primary surgeon to load and tamp the graft material into place.
There continues to be a need for further development and advancement in this field. For instance, in disclosure PCT publication WO 2014/158680 (incorporated by reference herein) FIG. 32 shows a cannula that extends thru the side wall of an implant device to introduce the bone graft material but no specific device or method is disclosed.